212 COMPOSITE. (composite family.) 



sected leaves, and inconspicuous greenish or whitish flowers. ('A/t/3po(n'a, the 

 food of the gods, an ill-chosen name for these worthless and coarse weeds.) 



§ 1. Sterile heads sessile, crowded in a dense cylindrical spike, the top-shaped involucre 

 with the truncate margin extended on one side into a large, lanceolate, hooded, 

 recurved, bristly-hairy tooth or appendage ; fertile involucre oblong and 4-angled. 



1. A. Mdcntafa, Michx. Hairy (l°-3° high), very leafy; leaves al- 

 ternate, lanceolate, partly clasping, nearly entire, except a short lobe or tooth 

 on each side near the base. (J) — Prairies of Illinois and southward. Aug. 



§ 2. Sterile heads in single or panicled racemes or spikes, the involucre regular. 

 # Leaves opposite, only lobed: sterile involucre 3-ribbed on one side. 



2. A. trifida, L. (Great Ragweed.) Stem square, stout (4°-12 e ' 

 high), rough-hairy, as are the large deeply 3-lobed leaves, the lobes oval-lanceo- 

 late and serrate ; petioles margined ; fruit obovate, 6-ribbed and tubercled. ® 

 — Var. integrifolia is only a smaller form, with the upper leaves or all of 

 them undivided, ovate or oval. — Moist river-banks ; common. Aug. 



* * Leaves many of them alternate, once or twice pinnatijid. 



3. A. artemisisefdlia, L. (Roman Wormwood. Hog-weed. Bit- 

 ter-weed.) Much branched (l°-3° high), hairy or roughish-pubescent ; 

 leaves thin, twice-pinnatifid, smoothish above, paler or hoary beneath ; fruit obo- 

 void or globular, armed with about 6 short acute teeth or spines. Q) — Waste 

 places everywhere. July - Sept. — An extremely variable weed, with finely 

 cut leaves, embracing several nominal species. 



4. A. psiloStsBCiiya, DC. Paniculate-branched (2° -5° high), rough 

 and somewhat hoary with short hispid hairs ; leaves once pinnatifid, thickish, the 

 lobes acute, those of the lower leaves often incised ; fruit obovoid, without tuber- 

 cles or with very small ones, pubescent, (ij (A. coronopifolia, Torr. §• Gr.) — 

 Prairies and plains, Illinois and southwestward. Aug. 



31. XANTHIUM, Tourn. Cocklebur. Clotbur. 



Sterile and fertile flowers occupying different heads on the same plant ; the 

 latter clustered below, the former in short spikes or racemes above. Sterile 

 involucres and flowers as in Ambrosia, but the scales separate. Fertile invo- 

 lucre closed, coriaceous, ovoid or oblong, clothed with hooked prickles so as to 

 form a rough bur, 2-celled, 2-flowered ; the flowers consisting of a pistil witti a 

 slender thread-form corolla. Achenia oblong, flat ; destitute of pappus. ~ 

 Coarse and vile weeds, with annual roots, low and branching stout stems, and 

 alternate toothed or lobed petioled leaves. (Name from £dv0os, yellow, in allu 

 sion to the color the plants are said to yield.) 



1. X. striiinariitm, L. (Common Cocklebur.) Rough; stems un- 

 armed; leaves dilated-triangular and more or less heart-shaped, on long petioles, 

 toothed and cut or obscurely lobed; fruit oval or oblong (h -§' long), pubes- 

 cent on the lower part of and between the hooked prickles, and with two strong 

 and usually straight beaks at the summit. — Barn-yards, &c. (Nat. from Eu ) — 

 Varies into forms with more spotted stems, and often larger fruit (§'-1' long), 



